The present invention relates to a fluid ejection device to be used in a printhead of an ink jet printer for ejecting fluid, such as ink, in a well-controlled manner, and a process for the production thereof.
With the development of a computerized society in recent years, demand for office automation or OA devices has been growing rapidly. Under such circumstances, demand for various kinds of printers has become increasingly stronger, not only with respect to their performance as a recording means but for higher-speed printing and improved picture quality.
In widely used ink jet printers, the ink jet printhead of the on demand system which enables a high-speed ejection of the ink at the user""s will, is critical for the performance of the printer. The ink jet printhead, in general, comprises an ink channel, a pressure chamber where ink is pressurized, a pressurizing means for the ink such as an actuator, and an ink outlet through which the ink is ejected. To realize an on-demand ink jet printer system, a pressurizing means with high controllability is required. Most conventional systems employ a bubble ejecting method, also known as a heating method, whereby the ink is heated to produce bubbles that eventually eject the ink, or a piezoelectric method, in which ink is directly pressurized by a deformation of a piezoelectric ceramic or the like.
FIG. 11 is a sectional perspective view showing an example of the construction of a conventional ink jet printhead. The conventional ink jet printhead consists of a piezoelectric member 111, a pressure chamber 112, an ink channel 113, an ink outlet 114, a fluid (ink) inlet 115, a first structure member 116, a second structure member 117, a third structure member 118, a diaphragm 119 and individual electrodes 120.
On a first side of the piezoelectric member 111, individual electrodes 120a, 120b, and so on are formed thereon. On a second side thereof electrodes are also formed in the same manner, 120au, 120bu, and so on. The piezoelectric member 111 is bonded to the diaphragm 119 via the electrode on the second side.
The diaphragm 119 and the first structure member 116, the second structure member 117 and the third structure member 118 are bonded by an adhesive or similar material, thereby forming a laminated structure. The pressure chamber 112 and the ink channel 113 comprise a cavity in first structure member 116. In general, a plurality of sets, each set comprising a the pressure chamber 112, an ink channel 113 and individual electrodes 120 are formed and disposed such that each set is separated from the other sets. The second structure member 117 is similarly formed with a plurality of separate ink inlets 115. Third structure member 118, comprising a plurality of separate ink outlets 114, is aligned with the second structure member so that the outlets align with the pressure chambers 112. The ink is supplied through the ink inlet 115, filling the ink channel 113 and the pressure chamber 112 with ink.
The diaphragm 119 is made of a conductive material and is in conductive communication with the electrodes 120au, 120bu, and so on mounted on the bonded surface of the piezoelectric member 111. Thus, if an electric voltage is applied between the diaphragm 119 and the individual electrodes 120a, 120b, and so on, diaphragm 119 conducts current and deforms, also deforming the section of the piezoelectric member 111 laminated to the diaphragm 119. Thus a selected section of piezoelectric member 111 and diaphragm 119 corresponding to each set of electrodes 120a, 120b, and so on can be deformed by selecting the set of electrodes to be energized with an electric voltage. The deformation pressurizes ink in the pressure chamber 112 underlying energized electrode 120a, for example, and the amount of ink responsive to the pressure is ejected from the ink outlet 114. The amount of deformation depends on the electric voltage applied to the piezoelectric member 111. Therefore, by controlling the magnitude of the electric voltage and the location at which the electric voltage is applied, the amount and location of the ink ejection can be arbitrarily changed.
The conventional thermal ink jet printhead, in general, is inferior to the piezoelectric method in terms of the response speed. On the other hand, a drawback of piezoelectric ink jet printheads is that the displacement of the piezoelectric member and the diaphragm is restricted by the thickness of the piezoelectric member. If the piezoelectric member is too thick, insufficient displacement may be provided due to the rigidity of the piezoelectric member itself. If the area of the piezoelectric member is increased to enlarge the displacement, the size of the ink jet printhead increases, making it difficult to achieve higher nozzle densities (the number of nozzles within a particular area). As a result, material cost increases. When the area of the piezoelectric member can not be increased, a higher driving voltage is required for a sufficient deformation.
Piezoelectric members with thickness of about 20 xcexcm have become available now through thick film forming and the integrated firing techniques, however, a higher nozzle density is still required for improved print quality. In order to reduce the area of the piezoelectric member to achieve a higher nozzle density, reduction of the piezoelectric member thickness is essential. However, conventional methods have limitations in this regard.
A cavity is typically provided within structures made of stainless steel or the like in order to form the ink channel, so for precise and complex ink channels, an increased number of layers may be required. Adhesive used on the bonded section is exposed to fluid for a long time, and therefore, reliability of the adhesive bond has always required close attention.
A fluid ejection device of the present invention includes at least one pressure chamber divided independently from other pressure chambers, an ink channel communicating with the pressure chamber, an ink outlet communicating with the pressure chamber, and a pressure generating section having a laminated body made of a piezoelectric material and an elastic body, the pressure generating section covering one face of the chamber. The pressure chamber, the ink channel and the ink outlet are defined by a structure comprising at least one planar silicon substrate bonded to at least one planar glass substrate.
A process for manufacturing the fluid ejection device of the present invention comprises the steps of: forming a through-hole for the pressure chamber and a through-hole for the ink inlet on a first substrate; bonding the first substrate to a second substrate; bonding the second substrate to a third substrate; and forming a pressure generating section comprising a laminated body including piezoelectric material and an elastic material such that the pressure generating section covering the through-hole for the pressure chamber with the pressure-generating section. The piezoelectric material may be a thin film material of PZT deposited by sputtering. The silicon substrates may be processed by reactive ion etching (RIE) and the glass substrates may processed by sand-blasting. The substrates may be directly bonded to one another by processing the surfaces and heating without the use of resin or other adhesives.
The configuration discussed above provides a thinner piezoelectric member, allowing a higher nozzle density. A plurality of silicon and glass substrates may be simultaneously finely processed by etching and sand-blasting, thereby improving processing precision and reducing the number of production steps. The silicon and glass substrates can be directly bonded, increasing the long-term reliability against inflow of fluid. Furthermore, multiple substrates can be bonded at one time, contributing to streamlining of the production processes.